Add Payment to an existing site

Would like to add PayPal or Stripe adaptive / authorize and capture payments or another checkout system to our restaurants' mobile ordering website. REQUIREMENTS: 1. Payment should be a. Authorize and Capture b. Split between restaurant, the restaurant's account for tips, and us. 2. At time of ordering, user should be able to a. Add a tip for servers (we will need buttons for 20%, 25% and 30%) b. Authorize payment c. Enter minimal information, especially if they've used the system before (i.e. cookies and express checkout) d. Not leave the website (if possible) 3. When restaurant confirms delivery of order by clicking a button on our web-based platform a. Payment should be captured. 4. When restaurant rejects / cancels an order by clicking a button on our web-based platform a. Payment should be canceled. 5. If possible, payment should be reversible even if it's been "captured" OTHER THINGS TO KNOW 1. Our custom site is written in PHP. PLEASE LET ME KNOW 1. Estimated time and cost 2. Portfolio / examples of work. 3. Anything else I should know.